This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. Section 119 from an application for DEVICE FOR CONTROLLING DATA FLOW IN ETHERNET AND METHOD THEREFOR filed in the Korean Industrial Property Office on Dec. 28, 1998 and duly assigned Serial No. 98-59206.
1. Field of the Invention
The present invention relates to an apparatus and method used for controlling the data flow of Ethernet hub in half-duplex mode.
2. Description of the Related Art
Ethernet LAN (Local Area Network) is a multiaccess, packet-switched network which uses a passive broadcast medium that provides the means to exchange data packets between the switches of Ethernet or between a data terminal equipment (DTE) and an Ethernet switch. The DTE is a data application device for transmitting and receiving the data packets by employing a communication protocol.
Ethernet as set forth in IEEE 802.3 is a standard protocol for a LAN with hubs at the center of the star configuration, with the wires radiating outward to connect the various network devices, which could include a plurality of DTEs connected thereto by unshielded, twisted paired (UTP) cables. As its name implies, the UTP cable resembles a telephone cable which consists of eight wires for connecting the plurality of DTEs to the hub. The UTP cable is also known as xe2x80x9c10 base Txe2x80x9d or xe2x80x9c100 base Txe2x80x9d depending on the network speed offered to each port by Ethernet hubs of 10 Mbps or 100 Mbps. The hub basically consists of a multi-port repeater for communicating with DTEs. However, the multi-port repeater indiscriminately allows the transfer of data packet destined to the intended DTE as well as the unintended DTE. Thus, it is difficult to maintain communication security and effectively use the available bandwidth.
In order to resolve above problem, a hub having a multi-port switch was developed to replace the multi-port repeater, as shown in FIG. 1. In FIG. 1, the hub 110 with the multi-port switching includes a plurality of ports connecting various DTEs (120_l to 120_n). The hub 110 detects for the destination address (DA) of a packet received through each input port to identify the destination port. After decoding the address, the switch sends the packet directly to its destination or sometimes stores the packet in its internal memory for an eventual transmission to the destination. However, in the store-and-forward architecture, if the number of the data packets stored in the internal memory increases beyond the memory capacity prior to transmission, the data can be lost. Accordingly, the data flow control of the hub 110 is needed to prevent such traffic overload. There are two types of data flow controls, one of which is a pause frame transmission method used in the full-duplex mode of MAC and the other is a back pressure method used in the half-duplex mode of medium access control (MAC).
The pause frame transmission method is specified in the IEEE802.3xc3x97 standard. If there is a traffic overload in the store-and-forward scheme, a control packet defined as a pause packet is sent to the DTEs to prevent any further transmission of the packet. This type of pause frame transmission method in the full-duplex mode is used for the paired connection between the switch and the DTE, between DTEs or between switches.
The above technique is not in the repeater, which uses the half-duplex mode. In the half-duplex mode, a jamming signal is sent to the transmission port to stop the transmission of the packets when the receiving port encounters the traffic overload. As illustrated in FIG. 2, if the packet memory (not shown) of the hub 110 reaches the traffic threshold and continuously receives the packets through the multiple input ports (not shown), the switch 210 of the hub regards this situation as a collision between the transmitted packet and the received packet. Upon such determination, a jamming signal generator 212 generates a jamming signal to prevent the transmission of data packets to a selector 216 via an overload signal line 220. The function of the selector 216 is to deliver the transmitted packets from the MACs 214 to the designated DTE. After receiving the jamming signal, the role of the selectors 216 is switched to delivering the jamming signal through the respective output-port 218 and the DTE to prevent the transmission of packets.
While the above method may control the packet generating sources by supplying the jamming signal to prevent the traffic overload, it also obstructs the transmission of local traffic relating to other terminals connected to the same repeater segment, thereby even preventing the packet transmission of some terminals not associated with the switch in the traffic overload problem. Thus, the jamming signals are delivered even to some terminals, which carry the local repeater traffic and which is not linked/processed by the overload switch.
It is an object of the present invention to provide an apparatus and method for controlling data flow of the Ethernet hub in a half-duplex mode in order to secure the local repeater traffic without being affected by the unrelated transmission interruption signal from the hub switching.
It is another object of the present invention to control the jamming signal to ensure the local repeater traffic from being affected by the jamming signal originated from the unrelated switch and still perform the data flow control of the Ethernet hub in a half-duplex mode.
According to the embodiment of the present invention, an apparatus is provided for controlling the data flow of the Ethernet hub in a half-duplex mode which includes a switch to control the data packets flow through a plurality of communication ports, the apparatus comprising a destination address (DA) detector for detecting the DA of a data packet received through the input-port of the communication port to determine whether the packet is to be treated by the switching hub; a logic gate for generating a selection signal based on the determination of the DA detector and an overload signal supplied by the switch indicating traffic overload; a jamming signal generator for generating a jamming signal for preventing the transmission of data packets in response to the selection signal, an MAC for converting the packet into a bit stream to be transferred according to the Ethernet protocol as set forth in a carrier-sense multiple access with collision detection (CSMA/CD); and, a selector for selectively delivering either the jamming signal or the packet from the MAC in response to the selection signal.
According to the embodiment of the present invention, a method is provided for controlling data flow of a Ethernet hub in a half-duplex mode having a switch to control the data packets flow through a plurality of communication ports. The method includes the following steps: detecting a destination address of an incoming data packet received through an input-port of the communication port to determine whether the incoming data packet is to be processed by said switch; generating an overload signal when the switch is overloaded; generating a selection signal in response to a determination that the incoming data packet is to be processed by the switch and that the overload occurs in the switch; generating a jamming signal to prevent the transmission of the data packets in response to the generated selection signal; and, selectively transmitting one of the generated jamming signal and the data packets to an output-port of the communication ports in response to the selection signal.